Heat Coefficient Research Articles

A study on performance characteristics of vapor injection heat pump cycle with indirect heat recovery

This paper proposes a vapor injection heat pump cycle with indirect heat recovery, which adds a sub-cooler and an evaporator on the basis of conventional vapor injection heat pump cycle. In the added first sub-cooler, refrigerant exchanges heat with outdoor fresh air entrancing into indoor for improving the indoor air quality, which increases the temperature of the outdoor fresh air and the subcooling of refrigerant. In the added high-temperature evaporator, refrigerant absorbs the heat from indoor exhaust air through heat exchange, which can improve the heating capacity and the cycle performance. The refrigerant R32 is selected as the working fluid to analyze the performance of the cycle. The results show that under the same operating conditions, the volumetric heating capacity of the cycle is increased by 33%–72% and the coefficient of performance is improved by 20.5%–33.5% compared with the conventional sub-cooler vapor injection heat pump cycle. When the outdoor ambient temperature is lower, the improvement ratios of volumetric heating capacity and coefficient of performance is larger. Therefore, this novel cycle is suitable to be used at the lower ambient temperatures. In addition, the larger fresh air ratio can bring better cycle performance.

Numerical analysis and correlation of thermohydraulic characteristics of louvered fin-tube heat exchanger

Louvered fins are compact heat exchangers that have a high heat-transfer area compared to their volume. The interrupted surface of a louvered fin improves heat transfer by repeating the disruption and regeneration of the boundary layer generated by the flow. The current study presents the empirical correlations between the heat and friction coefficient according to geometric parameters using a numerical approach. The proposed empirical correlations that include the flow depth are more accurate than those that do not contain the flow depth. Additionally, this study presents the process of developing a numerical simulation. The simulated and experimental results were compared, and both the friction f factor and Colburn j factor exhibited high accuracy, with errors within ±9%. The verified simulation produced heat transfer and friction results for each heat-exchanger geometry. Empirical correlations were developed based on the data obtained from the simulation, and 91% and 87% of the f and j factors exhibited error within ±10% with the simulation data, respectively. This enabled the development of empirical correlations for thermohydraulic characteristics that can be applied to the design of a compact heat exchanger with louvered fins, and suggestions for the optimal design of each parameter were presented.

Studying transient heat transfer in a cylindrical pin fin with radiation and convection

A simple experimental fin device was used to develop a laboratory procedure for undergraduate engineering students, in order to enhance their understanding of the transfer of thermal energy. This experiment exposes the student to several important concepts, namely one-dimensional, time-dependent heat transfer in extended surfaces by conduction, convection and radiation. In a few simple steps, students have the opportunity to compare the measured to the predicted temperature profiles obtained at different times using an analytical complex solution and to calculate convective and radiative heat coefficients, such as the relative predominance of convection heat transfer with respect to radiation.

Heat and Mass Transport Analysis of MHD Rotating Hybrid Nanofluids Conveying Silver and Molybdenum Di-Sulfide Nano-Particles under Effect of Linear and Non-Linear Radiation

This article is an attempt to explore the heat transfer features of the steady three-dimensional rotating flow of magneto-hydrodynamic hybrid nanofluids under the effect of nonlinear radiation over the bi-directional stretching surface. For this purpose, two different nano-particles, namely silver (Ag) and molybdenum di-sulfide (MoS2), were selected. Three different conventional base fluids were utilized to form desired hybrid nanofluids such as water (H2O), engine oil (EO), and ethylene glycol (EG). We obtained steady three-dimensional highly nonlinear partial differential equations. These highly nonlinear partial differential equations cannot be solved analytically, so these equations were handled in MATLAB with the BVP-4C technique with convergence tolerance at 10−6. The graph depicts the effect of the magnetization effect, thermal radiation, and stretching ratio on rotating hybrid nanofluids. Additionally, the impact of thermal radiation on the heat coefficient of three different hybrid nanofluids is being investigated. The augmentation in magnetization decreases the primary velocity, whereas the increment in radiation enhances the primary velocity. The stretching ratio and the presence of higher magnetic forces increase the temperature profile. The concentration profile was enhanced with an increment in the magnetic field, stretching, and rotation ratio. The maximum Nusselt number was achieved for the Ag-MoS2/EO hybrid nanofluid. It was concluded that augmentation in nonlinear radiation enhances the heat transfer coefficient for the examined cases (I) and (II) of the hybrid nanofluids. The Nusselt number doubled for both the examined cases under nonlinear radiation. Moreover, it was discovered that Ag-MoS2/water produced the best heat transfer results under nonlinear radiation. Therefore, the study recommends more frequent exploration of hybrid nanofluids (Ag-MoS2/water) when employing nonlinear radiation to analyze the heat transfer coefficient.

A Package of Momentum and Heat Transfer Coefficients for the Stable Surface Layer Extended by New Coefficients over Sea Ice

The bulk transfer coefficients of momentum, heat, and humidity belong to the main ingredients of numerical weather prediction and climate models. They are needed for the calculation of turbulent fluxes in the surface layer and often rely on the Monin–Obukhov similarity theory requiring universal stability functions. The problem of a derivation of transfer coefficients based on different stability functions has been considered by many researchers over the years but it remains to this day. In this work, dedicated to the memory of S.S. Zilitinkevich, we also address this task, and obtain transfer coefficients from three pairs of theoretically derived stability functions suggested by Zilitinkevich and co-authors for stable conditios. Additionally, we construct non-iterative parametrizations of these transfer coefficients based on earlier work. Results are compared with state-of-the-art coefficients for land, ocean, and sea ice. The combined parametrizations form a package in a universal framework relying on a semi-analytical solution of the Monin-Obukhov similarity theory equations. A comparison with data of the Surface Heat Budget of the Arctic Ocean campaign (SHEBA) over sea ice reveals large differences between the coefficients for land conditions and the measurements over sea ice. However, two schemes of Zilitinkevich and co-authors show, after slight modification, good agreement with SHEBA although they had not been especially developed for sea ice. One pair of the modified transfer coefficients is superior and is compatible to earlier SHEBA-based parametrizations. Finally, an algorithm for practical use of all transfer coefficients in climate models is given.

Inheritance factor on the physical properties in metallic glasses

Material genetic engineering can significantly accelerate the development of new materials. As an important topic in material science and condensed matter physics, the development of metallic glasses (MGs) with specific properties has largely been the result of trial and error since their discovery in 1960. Yet, property design based on the physical parameters of constituent elements of MGs remains a huge challenge owing to the lack of an understanding of the property inheritance from constitute elements to the resultant alloys. In this work, we report the inherent relationships of the yield strength σ y, Young’s modulus E, and shear Modulus G with the valence electron density. More importantly, we reveal that the electronic density of states (EDOSs) at the Fermi surface (E F) is an inheritance factor for the physical properties of MGs. The physical properties of MGs are inherited from the specific element with the largest coefficient of electronic specific heat (γi ), which dominates the value of the EDOS at E F. This work not only contributes to the understanding of property inheritances but also guides the design of novel MGs with specific properties based on material genetic engineering.

Insulator–metal phase transition in novel Sr2OsTiO6 double perovskite via doping - Computational FP study

The structural, electronic, bonding, magnetic, optical and thermal properties of parent perovskite namely SrTiO3 (STO) and novel double perovskite namely Sr2OsTiO6 (SOTO) compounds are analyzed by using Full Potential (FP) - Linearized Augmented Plane Wave (LAPW) method through WIEN2K code. The optimized lattice parameter, bond length, bond angles, Fermi energy (EF), Density of States (DOS) at Fermi Level (FL), electronic specific heat coefficient are computed for the optimized STO and SOTO compounds. At ambient condition SrTiO3 is behaving as a semiconductor with a band gap 1.966 eV and via doping of SrOsO3 and SrTiO3, the resultant product of double perovskite phase namely Sr2OsTiO6 is shifted from the semiconductor state to a normal conductor state. Electron density plots, band structure plots and DOS are illustrated and compared for both STO and SOTO compounds. Diverse bonding and electronic band characteristics are noted and compared. Our band structure calculation results are reveal that the possibility of Electronic Topological Transition (ETT) in these compounds under the effect of doping. Since there is a predominant variation over the structural, electronic and magnetic properties of double perovskite even though not much variation over their mechanical properties. To illustrate the illumination properties of the compounds under study, the optical properties are also analyzed. Hence this study helps to lead the complete examination of suitable photovoltaic properties of STO and SOTO compounds.

Analysis of a modified transcritical CO2 two-stage ejector-compression cycle for domestic hot water production

High-efficiency domestic hot water (DHW) production has gained more attention currently, and a modified transcritical CO2 ejector enhanced two-stage compression cycle (METC) for the DWH production is proposed in this study. To investigate the applied potential of the modified cycle, the validated theoretical models are constructed to compare and analyze the performance between the METC system and the basic transcritical CO2 two-stage vapor compression cycle (BTC) under different operating conditions. The results show that the system METC outperforms the system BTC in terms of the heating coefficient of performance (COPH), system total heating capacity (Qtot), and the exergy efficiency (ηII) under different conditions. Compared with the system BTC, the COPH, Qtot, and ηII of the system METC are improved by 12.1%, 15.7%, and 15.3% under a typical operating condition. The ejector improves the refrigerant mass flow rate and absorption of heat in the evaporator. The low-grade working fluids are converted to a mid-grade state via the ejector, which is condensed in a mid-temperature heat exchanger to preheat the domestic hot water. Besides, the ejector reduces the exergy consumption and improves the system’s exergy efficiency. The proposed cycle promotes the further improvement of the transcritical CO2 two-stage compression cycle for DHW production.

Heat flux estimation of the cylinder in hypersonic rarefied flow based on neural network surrogate model

An efficient method to predict thermal loads on hypersonic vehicles in rarefied flows is immediately needed, especially when designing the thermal protection system. To meet the demand, we combine artificial neural networks with the direct simulation Monte Carlo method and build the surrogate model for hypersonic rarefied flows with three inputs (Knudsen number, temperature ration, and Mach number). The heating coefficients at nine points along the surface of a two-dimensional cylinder are output from the model. The results at the stagnation point have errors within 3%, while the biggest error of nine points is 4.8%. The heating coefficients are also compared with the bridge function’s, whose errors reach 14% at the stagnation point and 20% along the surface. The reasons for the errors are discussed in detail. In addition, this framework of building the model with artificial neural networks can be extended to solve problems with more complex mechanisms or configurations.

Surrogate models for lithium-ion battery heat generation based on orthogonal experiments by eliminating external wire connection effect

• Maximum overestimation of 39.9% in heat generation occurs due to the wire connection at 40 °C and discharge rate of 3C. • Heat generation rate is determined by C-rate, temperature and depth of discharge with ranking order of DR > T > DOD. • Average deviation of 6.90% was obtained between present surrogate model and experimental tests beyond 0.53 W. • Heat generation model of the battery was verified by comparing with experiment measurement under natural convection. In this paper, an experimental investigation on the heat generation rate is presented for the cylindrical lithium-ion batteries under different operation conditions such as changing temperature and depth of discharge by eliminating the external connection effect. The tests were conducted by placing the battery in the thermostat chamber and connecting to the charger instrument through external wires. The intermediate quantities including the overpotential, entropy heat coefficient and internal resistance were obtained by the corresponding orthogonal test in full matrix design. It is found that the maximum overestimation of 39.9% occurs at the highest temperature of 40 °C and discharge rate of 3C with the wire connection. As such, the wire connection effect must be examined and eliminated in the heat generation estimation. The consequent sensitivity analysis indicates that the discharge rate has the largest impact on the heat generation of battery, followed by the temperature and depth of discharge, namely, DR > T > DOD. The temporal heat generating surrogate models of the battery are correlated under different operation conditions with the depth of discharge, temperature, and discharge rate by the response surface analysis, which agrees with experiment results within 6.90% for heat generation rate beyond 0.53 W corresponding to the 1C discharge case. Moreover, the heat generation model is verified by comparing the numerically obtained battery temperature with experiment measurement under natural convection condition. The temporal temperature rise of the battery during actual operation conditions such as worldwide harmonized light vehicles test procedure (WLTP) can be estimated based on the present surrogate models.

Antiferromagnetic order in Yb4Ru7As6 with the cubic U4Re7Si6-type structure

We investigated the electronic properties of Yb4Ru7As6 using single crystalline samples grown by the Bi-flux method. Yb4Ru7As6 crystallizes in the cubic U4Re7Si6-type structure. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that Yb4Ru7As6 orders antiferromagnetically below the Néel temperature of 2.5 K with the moderately enhanced electronic specific heat coefficient of 120 mJ/(Yb-mol⋅K2). A rapid increment in magnetization of about 0.25 μB/Yb has been detected at low magnetic field below 4 K, implying a weak ferromagnetic component.

Experimental investigation of the performance of the plate heat exchanger using (Multi-Walled Carbon Nanotubes–Al2O3/water) hybrid nanofluid

Heat exchanger development is one of the issues where study continues because of its relevance in a variety of sectors. The utilization of hybrid nanofluids as a working fluid requires more investigation. The performance of plate heat exchangers (PHEs) employing hybrid nanofluid (multi-walled carbon nanotubes (MWCNTs)–Al2O3/water) with varying volume concentrations was investigated in an experimental investigation. The current study makes use of an Armfield PHE (HT32) with an Armfield heat exchange service unit (HT30X). In this investigation, three-volume concentrations were employed (0.5%, 1%, and 2%). A (MWCNTs/water) nanofluid with a volume concentration of 2% was prepared to compare with the hybrid nanofluid. The heated fluid (distilled water and nanofluids) has a Reynolds number of 100 to 800. By monitoring the variables, the overall heat transfer coefficient, pressure drop, friction factor, mean Nusselt number, and effectiveness could be computed. Based on the concentration of nanoparticles in the base fluid, the experimental findings revealed that hybrid nanofluids had a substantial impact on the heat transfer process. With increasing volume concentration, the overall heat coefficient, Nusselt number, and effectiveness increase. The volume concentration of nanoparticles determines the increase in the overall heat coefficient from 6% to 97% compared to pure distilled water. The increase in the hybrid nanofluids volume concentration leads to an increase in the pressure drop and the friction factor. The Nusselt number and the effectiveness increase with the increase of the volume concentrations and Reynolds number. Comparing the performance of the hybrid nanofluid and monoparticles nanofluid with the same concentration ratio, an improvement in performance was seen using hybrid fluids. An empirical correlation to calculate the Nusselt number for the hybrid nanofluid (MWCNTs–Al2O3/water) with the ratio of the particles (50:50) is obtained. It is possible to discover acceptable agreement by comparing the current study to earlier publications on this subject.

Applicability of Temperature Discrete Equation to NMRF Boundary Layer Scheme in GRAPES Model

By deriving the discrete equation of the parameterized equation for the New Medium-Range Forecast (NMRF) boundary layer scheme in the GRAPES model, the adjusted discrete equation for temperature is obviously different from the original equation under the background of hydrostatic equilibrium and adiabatic hypothesis. In the present research, three discrete equations for temperature in the NMRF boundary layer scheme are applied, namely the original (hereafter NMRF), the adjustment (hereafter NMRF-gocp), and the one in the YSU boundary-layer scheme (hereafter NMRF-TZ). The results show that the deviations of height, temperature, U and V wind in the boundary layer in the NMRF-gocp and NMRF-TZ experiments are smaller than those in the NMRF experiment and the deviations in the NMRF-gocp experiment are the smallest. The deviations of humidity are complex for the different forecasting lead time in the three experiments. Moreover, there are obvious diurnal variations of deviations from these variables, where the diurnal variations of deviations from height and temperature are similar and those from U and V wind are also similar. However, the diurnal variation of humidity is relatively complicated. The root means square errors of 2m temperature (T2m) and 10m speed (V10m) from the three experiments show that the error of NMRF-gocp is the smallest and that of NMRF is the biggest. There is also a diurnal variation of T2m and V10m, where T2m has double peaks and V10m has only one peak. Comparison of the discrete equations between NMRF and NMRF-gocp experiments shows that the deviation of temperature is likely to be caused by the calculation of vertical eddy diffusive coefficients of heating, which also leads to the deviations of other elements.

Applying a numerical optimization to determine the entropic heat coefficient of a battery

The quality of modeling the thermal behavior of a battery also depends on the accuracy of the entropic heat coefficient (EHC) applied. The EHC has so far been experimentally determined using time-consuming measuring methods. This paper shows the application of a method determining the EHC based on experiments and numerical optimization. The applied practical steps to determine the EHC are presented and discussed. This method provides sufficiently accurate results for practical applications within a relatively short time (within six days). The simulations and measurements for the validation were performed simultaneously on a Hardware-in-the-Loop test bench. At the beginning of each experiment, the characteristic maps for the battery module’s electrical simulation were unknown and then determined simultaneously online. The simulation results compared to the simultaneously recorded measurement data of different dynamic test scenarios (about one hour each) show a temperature difference of at most 0.4 K, with an overall increase of 3.9 K. Furthermore, the results show that the influence of the EHC contributes significantly to the resulting temperature curve and should not be neglected in thermal analyses of a battery: Deviations of up to 38 % in the temperature values have been shown when the EHC is not considered. • First practical use of a numerical determination of the Entropic Heat Coefficient. • Validation of the numerical determination of the EHC within an application example. • Demonstrate the importance of the EHC in describing the thermal behavior of a battery. • Applying a universal thermal 0D model for the thermal description of a battery module. • Parameter setting of a 0D model describing the thermal behavior of a battery module.

Estimation of heat transfer model parameters by using recursive least square (RLS) method for a shape memory alloy wire

The thermal model of shape memory alloy (SMA) wires is improved by identifying the convectional heat transfer model (htm) parameters. Recursive Least Square (RLS) Method is used to estimate heat transfer coefficient, specific heat and latent heat coefficient. The parameters are estimated altogether with the surface area, volume and density of the wire. Also, after measuring the resistance by using multimeter, the value of each parameter was separately determined. Heat transfer coefficient is ambient dependent and dominant in the heat transfer model. The estimation of heat transfer coefficient is important and this is shown in this study. The proposed method builds an improved heat transfer model for SMA wire by using a single set of experimental data. Performance of the estimation with RLS is validated by using the measured data. It is shown that heat convection coefficient can be estimated with high accuracy. Thus, it is revealed that addition of the latent heat term during phase transformation into the model resulted in a more accurate model. The accuracy of the model can be enhanced by 28% by the addition of latent heat term.

Homotopic framework for the Buongiorno model of 2D viscoelastic nanofluid flow toward a porous curve surface with ohmic heating and Brownian diffusion effects

The present investigation explores the impacts of heat transfer in a two-dimensional flow of a viscoelastic nanofluidic flow over a penetrable channel. The consequences of internal heat generation/absorption, viscous dissipation, thermal diffusivity, and joule heating accompanied by variable properties of the nanoliquid are considered in the model flow laws. With the aid of suitable transformation inequalities, the boundary layer partial differential (PDEs) reduces to governing coupled nonlinear ordinary differential equations convenient for computation. Using MATHEMATICA syntax, a programming algorithm, the analytical homotopic scheme is imposed explicitly for attaining the dimensionless solutions of fundamental equations. The attained numerical outcomes are analyzed for diversified parameters on different flow fields. The convergence and stability criterion is established for the precision of the governing parameters. The present work has dynamic prominence in medicine and engineering, which develops interest among young researchers. In addition, the impression of system parameters on drag force, heat, and mass flow coefficient with 3D graphs is also debated. The comparison is done and acquired results show that they are in remarkable agreement with the numerical method.

Numerical simulation of the thermal performance of a wavy fin configuration for a straight fin array

Fins over the years have been used as heat exchangers for exchanging heat generated in engineering machines or systems, between the system surface and the ambient air. However, the challenge of thermal design for the best geometry of heat fin prompted the study, to determining the performance of a wavy and straight fin projecting vertically from a horizontal base, by comparing their rate of heat transfer. In this study a free convection steady state numerical analysis was carried out using Solidworks 2018 flow simulation application, which is based on finite volume method of Computational Flow Dynamics (CFD). The numerical analysis was carried out on three different fin array configurations, all of the same fin spacing or separation distance. The three fin array modeled includes the straight and wavy fin of fin height, 35mm and spacing, 14.2mm respectively. The third fin was a straight fin of height, 50mm equivalent of the effective wavelength of the wavy fin, but of same fin spacing. Aluminum metal was selected as the material, and the simulation was done using air as the fluid, of temperature, and convective heat coefficient, 27°C and 20W/mK respectively. Simulation was carried out at different temperatures for each geometry, ranging from 45°C – 120°C. The results showed that the difference in the rate of heat transfer for the wavy fin and straight fin were close at low temperatures, but significantly increased to about 28% at higher temperatures in favor of the wavy fin. The third fin had an insignificant 9% heat transfer rate higher than the wavy fin but with 43% additional height, thereby occupying more space. It is established from this study that wavy fin array possesses higher convection heat transfer performance than the straight rectangular fin array. Therefore, in a bit to achieve high performance heat transfer with limited space, a wavy fin array is recommended.

Energy, exergy, economic and environmental analyses and optimization of a novel vapor injection autocascade heat pump for high-temperature water heating

Aiming to develop a high-efficiency and low-cost high-temperature heat pump with large temperature lift ability, a novel vapor injection autocascade heat pump for high-temperature water heating is proposed in this paper. The proposed system utilizes the vapor injection technique to improve the limited performance of the conventional autocascade system and can achieve outstanding heating performance with over 100 °C heating temperature. The energy, exergy, economic and environmental performance of the proposed system are investigated by simulation method and compared with those of the conventional autocascade heat pump. The proposed system averagely improves the heating coefficient of performance and capacity by 51.8% and 104.3% over the conventional system when the evaporating temperature ranges from 0 °C to 20 °C, respectively. The exergy analysis indicates that the excellent exergy performance of the proposed system mainly benefits from the irreversible loss reductions in the throttling valves and cascade condensers. The proposed system possesses the lowest energy cost except for the coal-fired boiler, and produces the minimum pollutant emission except for the gas-fired boiler. The heating coefficient of performance of the proposed system is improved by 12.4% ∼ 14.0% through single-objective optimization. The optimal coefficient of performance and levelized cost of energy are 2.59 and 0.070 $ kWh−1, respectively.

Peristaltic pump with heat and mass transfer of a fractional second grade fluid through porous medium inside a tube

In magnetic resonance imaging (MRI), this MRI is used for the diagnosis of the brain. The dynamic of these particles occurs under the action of the peristaltic waves generated on the flexible walls of the brain. Studying such fluid flow of a Fractional Second-Grade under this action is therefore useful in treating tissues of cancer. This paper deals with a theoretical investigation of the interaction of heat and mass transfer in the peristaltic flow of a magnetic field fractional second-grade fluid through a tube, under the assumption of low Reynolds number and long-wavelength. The analytical solution to a problem is obtained by using Caputo's definition. The effect of different physical parameters, the material constant, magnetic field, and fractional parameter on the temperature, concentration, axial velocity, pressure gradient, pressure rise, friction forces, and coefficient of heat and mass transfer are discussed with particular emphasis. The computed results are presented in graphical form. It is because the nature of heat and mass transfer coefficient is oscillatory which is following the physical expectation due to the oscillatory nature of the tube wall. It is perceived that with an increase in Hartmann number, the velocity decreases. A suitable comparison has been made with the prior results in the literature as a limiting case of the considered problem.

Analysis of the Air-Reversed Brayton Heat Pump with Different Layouts of Turbochargers for Space Heating

The air-reversed Brayton cycle produces charming, environmentally friendly effects by using air as its refrigerant and has potential energy efficiency in applications related to space heating and building heating. However, there exist several types of cycle that need to be discussed. In this paper, six types of air-reversed Brayton heat pump with a turbocharger, applicable under different heating conditions, are developed. The expressions of the heating coefficient of performance (COP) and the corresponding turbine pressure ratio are derived based on thermodynamic analysis. By using these expressions, the effects of turbine pressure ratio on the COP under different working conditions are theoretically analyzed, and the optimal COPs of different cycles under specific working conditions are determined. It is observed that Cycles A and C have the highest heating COPs, and there is an optimal pressure ratio for each cycle. The corresponding pressure ratio of the optimal COP is different, concentrated in the range of 1.5–1.9. When the pressure ratio reaches the optimal value, increasing the pressure ratio does not significantly improve the heating COP. Take Cycle F as an example: the maximum error between the calculated results and experimental observation is lower than 5.6%. These results will enable further study of the air-reversed Brayton heat pump with a turbocharger from a different perspective.